Archive for Aussois

approximately Bayes [on Skye]

Posted in Mountains, pictures, Running, Statistics, Travel, University life with tags , , , , , , , , , , , , , , , , , , , , , , , , , , , , on May 28, 2026 by xi'an

Wow, what an exciting workshop in an equally exciting place! Strong themes were post-Bayes (Gibbs priors, martingale priors, predictive Bayes, &tc.) and deep neural network modelling. With animated discussions allowed by the free windows planned in the program. And the very early dinner at Sabhal Mòr Ostaig that let a long sunlit evening for impromptu Q&A’s [with a serving of lamb and another of haggis pie!]. Making me realise the large corpus of work I had missed in the past years on these topics, even though the satellite of BayesComp last year was already an eye opener. (Stay tuned for news about BayesComp 2027 & its mirror in Aussois!) The proposal in Jeff Miller’s discussion of Jeremias Knoblauch’s overview of post-Bayes [I’d rather favour another name!]  to consider directly likelihood values as the data was particularly appealing to me, while reminding me of the foundations of nested sampling. (Hopefully, a new perspective on uncertainty assessment for nested sampling is soon to be completed!)

On the non-academic side, the long days in The North helped with my running with above 90km bagged in the week (and no downpour on the runs). But little to my swimming since the water was cold enough to limit my laps to 5mn each time! Paradoxically the worst day was the one I chose for climbing the Inaccessible Pinnacle (as expanded in another ‘Og entry).

Nature on mirror conferences

Posted in Books, Statistics, University life with tags , , , , , , , , , , , , , , , , , , , , , , , on January 28, 2026 by xi'an

In a news article entitled “Scientists skip key US meetings — and seize on smaller alternatives”, Nature discusses the impact of the restrictive policies put in place by the Trump administration on US conferences and their attendance. Including the multiplication of mirror and satellite meetings. One of the examples in the article is Neurips 2025,

“…the artificial-intelligence conference NeurIPS hosted not only its main meeting in San Diego, California, but also its first-ever alternative location, in Mexico City, with the goal of alleviating travel challenges (…) in response to “skyrocketing attendance and difficulties in obtaining travel visas some attendees have experienced in the past few years when only one location was available” [while] a group of AI researchers in Europe organized an independent spin-off conference, dubbed EurIPS, in Copenhagen (…) owing to concerns including climate change [and people expressing] a desire for a less hostile environment”

With a limited number of 500 participants attending in Mexico. And a massive number in Copenhagen, over 2,000! With a final quote from Emtiyaz Khan (a plenary speaker at ISBA 2026):

“[I] chose to travel to EurIPS rather than NeurIPS because of the difficulties many others faced in getting into the United States. The smaller nature of EurIPS made it much easier to meet and interact with other scientists. I absolutely loved it and I would love to see it happen again.”

This state of affairs is not going to vanish with Trump adding more countries to the banned country list, 75 at this stage!, and this is a call to arms for ISBA and IMS conference organisers towards planning for multi-hub configurations, since such international organisations cannot exclude a third of the countries in the World from attending their conferences. Which makes our current ISBA survey all the more relevant! I am currently building a mirror meeting for BayesComp 2027 in Aussois, French Alps. For those who cannot or do not wish to travel to Texas for the main conference.

last light in Maurienne [jatp]

Posted in Mountains, pictures, Travel with tags , , , , , , , , on December 7, 2025 by xi'an

Gaussian mixture via continuous sparse regularization

Posted in Books, Mountains, Statistics, University life with tags , , , , , , , , on December 6, 2025 by xi'an

There were several talks and posters in Aussois involving mixtures, incl. one by Romane Giard on a proposal recently posted on arXiv. The mixture is made of multivariate Gaussian components with unknown but diagonal covariance matrices. The number s of components is unknown as well. The estimation approach is based on a form of LASSO that relies on a point process representation of the mixture parameters, an approach long defended by Peter Green (as summarised in his introductory chapter for our Handbook of Mixture Analysis.  Which avoids unnecessary confusions about identifiability and label switching.

The procedure of estimation is thus (B-)LASSO, meaning a data fitting (or fidelity) term comparing a kernel density estimate (seen as a Gaussian convolution) to the smoothed predicted density. Plus a sparsity term, namely a total variation norm of the point process measure. The theoretical result requires a fixed minimum on the variances and a minimum distance between the component parameter vectors. Things get a bit more complicated (for me), given that the point process measure gets replaced by a weighted, approximate, version where each component is attributed a positive weight depending on the variance parameters uk of the Gaussians, a product of (uk²+τ²)-1/4 terms (with τ a regularising parameter). Since the paper is fully focussed on theoretical properties, it does not expand on the practical derivation of the estimator, acknowledging the numerical resolution of the minimisation problem is yet unknown, with a substitute “closer to a realistic algorithmic framework” (p20).

Back to Aussois, back to Vanoise!

Posted in Mountains, pictures, Running with tags , , , , , , , , , , , , , , , , on December 3, 2025 by xi'an

So wonderful to be back in Aussois, 20 years later! Same place, same reason, namely a meeting with young statisticians. (Plus the call of the mountains!) And same guide, Baptiste Damevin, as well! Who in the meanwhile got into a mountain accident the very same day I had my climbing accident, albeit a much more serious one since he was swept by an avalanche on the Dent Parrachée—Éric and I climbed with him in 2003—while ski touring, falling down more than 500m and surviving multiple fractures! Five other alpine touring skiers got caught as well, three of whom died. Baptiste did recover from injuries that should have left him permanently incapacitated and resumed his guiding and mountaineering activities. Kudos!!


Fortunately, he was available for a day hike and he took us (Julyan, Guillaume and I) to the Grand Aiguille Rousse (3482m) on a favourable (sunny and decently cold) day. While the hike was reasonably easy, with mostly hard snow, I was still tired from my earlier marathonian efforts and decided to turn back at 3000m before the steepest bits, in order to let the others get to and enjoy the summit. And return back to the car before dark.